This disclosure is directed to an apparatus or system which measures the rate of flow of leakage through a tear or perforation in the geomembrane. Liquid impoundments are made by scooping out a pond or lake, typically using earth moving equipment, and a geomembrane is spread across the pond. It is normally formed by joining multiple sheets of a thin plastic material. The material is perhaps a few mils thick. The sheet material is spread over the pond to define the bottom of the impoundment and marginal embankments which confine the liquid in the pond or impoundment. The soil beneath the geomembrane is prepared at least in some measure. For instance, sufficient quantities of clay may be available to form an almost impervious substrata which prevents leakage. In that event, even should a tear or perforation be made in the geomembrane, the leakage rate may be negligible. On the other hand, the subsoil beneath the geomembrane may be sandy and therefore a leak may have a substantial flow rate. Thus, the existence of a tear or perforation in the geomembrane is not necessarily related to the flow rate through the tear or perforation. In other words, the volumetric flow of liquid through the leak is variable and is dependent on many factors including the size of the leak, the nature of the soil beneath the geomembrane, saturation of the leaked liquid into the subsoil, and other factors.
Protection of the impounded liquid is very important. To this end, various and sundry devices have been devised for location of leaks. It is one thing to locate a leak, but it is another and separate factor to measure the volume of leakage fluid. The volume must be measured to determine whether or not the leak is a critical matter. The volume of flow cannot directly be inferred from the size of the tear or perforation. Accordingly, it must be measured independently of the size of the tear or perforation. This disclosure sets forth a flow measuring system.
The present invention is particularly useful in measuring the volume or flow rate in a leak through geomembrane. It is particularly successful with a geomembrane confining an impoundment of an electrically conductive liquid. The apparatus utilizes a type of inverted funnel. The wide end of the funnel includes a surround peripheral lip constructed with a lower edge having a weighted member therearound. This lower edge can be made pliant so that it conforms with the geomembrane contours. It is preferably somewhat wide, typically circular to enable it to encompass the area of the leak and adjacent regions. This seals off the region of the leak so that the leakage must then pass through the inverted funnel. The inverted construction terminates at an upper narrow inlet tube or passage. This functions as a venturi in that the flow rate of the liquid is accelerated through this narrow passage. On the exterior, there is arranged a magnetic system, ideally an electromagnet which forms a transverse magnetic field. The field is relatively long in that it preferably is formed at long magnetic poles to encompass the full length of the venturi system. A perpendicular pair of plates are positioned for measurement of voltage across the venturi within the magnetic field. This provides a voltage which is related to flow velocity as will be described in detail.